- 3306 - METEORITES - visits to learn origin of solar System? Scientists are studying ancient meteorite grains using a new analysis method. These grains, which are older than the solar system itself, formed in ancient stars that died before our sun's birth. Similar stars still exist in the universe and the analysis of these presolar grains provides an glimpse into the stars' chemistry.
------------- 3306 - METEORITES - visits to learn origin of solar System?
- Samples of the Murchinson meteorites, which showered 220 lbs. of cosmic rock onto the Australian town of Murchinson in 1969 are being studied These meteorites rained down and one of the largest pieces broke through the roof of a local barn somehow without injuring anyone.
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- "Murchinson is a primitive meteorite, which has formed at the beginning of the solar system and after its formation never melted. Most meteorites that come from the asteroid belt experience collisions and heating, which melts them so any pristine material from the early stages of the solar system disappears.
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- In the Murchinson meteorite, grains of rock older than the solar system were embedded in younger material. Scientists know from previous research that these grains pre-date the birth of the solar system because their chemical composition is different.
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- These grains are made of silicon carbide, silicon and carbon atoms. But silicon carbide doesn't naturally form in our solar system because we have a lot of oxygen around and all these carbon atoms would bond with oxygen first to form carbon oxide molecules.
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- The most likely origin of these grains are the carbon stars, bright red giant stars whose atmospheres contain more carbon than oxygen. Does the compositions of certain isotopes in the meteoric grains match those in the carbon stars?
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- Isotopes are varieties of the same chemical element that differ by the number of neutrons in their nucleus. While some isotope compositions are common in the solar system, others can only arise inside of specific types of stars.
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- Objects in our solar system have ratios of carbon 12 to carbon 13 of about 89 to 1. But these presolar grains have carbon 12 to carbon 13 ratios ranging from 2 to 200 to 1, which results from fusion reactions in their parent stars. The same applies for isotopes of nitrogen, aluminum and magnesium.
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- These isotopic compositions matched what observations revealed about carbon stars. These grains spent hundreds of million years in the interstellar medium, and billions of years in our solar system and as a result their surfaces may have absorbed these materials.
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- Scientists have devised a new analytical method designed to remove any material that may cling to the surface of these grains. As part of this technique, they first dissolved pieces of the Murchinson meteorite in acid until they were left only with the silicon carbide grains. They then showered the grains with beams of cesium and oxygen ions to get rid of any material that may have come from younger components of the meteorite.
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- Then they made spectroscopic measurements of the grains' isotope compositions. The results matched much more closely the data from carbon star observations. This showed that not only did these grains most likely come from carbon stars but also that they can now be used to help scientists advance their understanding of these types of stars
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- If the meteorites don’t come to us we can maybe send spacecraft to go visit them. Spacecraft have visited most pockets of the solar system by now, but a new region is about to come under robotic inspection, the two clumps of asteroids that flank mighty Jupiter in its orbit.
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- Although scientists have spotted thousands of “Trojan asteroids’ in these two swarms of meteorites and asteroids no mission has ever seen them up close. That will change in 2027, when spacecraft “Lucy” makes its first of five flybys .
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- NASA's $981 million Lucy mission is scheduled to launch on October 16, 2021, is a daring expedition that will make six carefully orchestrated flybys: one in the main asteroid belt, the rest among Jupiter's Trojans asteroids.
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- The mission's agenda of flyby visits eight of these intriguing space rocks. Lucy can't stay because orbiting an asteroid requires much more fuel than flying past. Instead, Lucy will become the first mission to make so many “flybys” in the outer solar system, and it will approach its targets at a hurtling pace of 3 to 6 miles per second. That's 10,800 to 21,600 mph.
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- Although the mission stretches over 12 years, Lucy will do the bulk of its work in a total of about 24 hours.
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- From Earth, scientists can't see much detail about any given Trojan. But between the two clumps of asteroids at Jupiter, astronomers have identified more than 10,000 bodies stuck in the gravitational parking spaces ahead of and behind the gas giant planet in its orbital track around the sun.
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- Scientists have noticed unusual diversity among these Trojan asteroids, particularly in terms of their color, which ranges from gray to quite red and is tied to expected differences in chemical makeup.
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- A better understanding the Trojans can sharpen scientists' picture of how the solar system came to be the way it is, with planets that seem impossible to form where they are found today.
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- New models suggests that the four giant planets formed relatively close to the sun then migrated outward, in the process scattering small pieces of debris like asteroids into the inner solar system.
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- The theory is that the different colors on display among the Trojans represent formation at different distances from the sun, with the migrating planets kicking them into the gravitationally stable regions ahead of and behind Jupiter.
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- The flybys observations include color photographs of the Trojans' surface, infrared spectrometry to identify different compounds on their surfaces and analysis of Lucy's communication signal from Earth that will tell scientists how dense each asteroid is.
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- One pair of asteroids is “Eurybates” and “Orus“ are both estimated to be about 40 miles wide. Eurybates is quite gray and likely rich in carbon. Orus is quite red and likely rich in organic materials.
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- Lucy will make these flybys on Aug. 12, 2027, and Nov. 11, 2028.
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- The first flyby, in April 2025 of another main belt asteroid, “Donaldjohanson”, in honor of the anthropologist who discovered the fossil that the Lucy mission is named for, a hominin who lived in what is now Ethiopia 3.2 million years ago.
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- The flyby is a bonus, the asteroid will be near the path that Lucy had to travel anyway on its journey out to the Trojans. It's one member of a clump of asteroids that are the fragments of a much larger space rock that was smashed to bits, a type of asteroid that scientists haven't seen before. And astronomers even know about when the collision in question occurred.
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- “Donaldjohanson” is very young, estimated between 100 and 200 million years, which makes it one of the youngest things in the solar system.
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- Lucy's first Trojan target is Eurybates, the gray component of the pair at the heart of the mission's design. It, like Donaldjohanson, is a fragment from an impact.
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- Scientists know that history because Eurybates is surrounded by a host of smaller pieces that trudge along a nearly identical orbit, the marker of a collision family.
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- In 2018, astronomers using the Hubble Space Telescope spotted a much smaller asteroid circling the main body of Eurybates, a tiny moon, with the discovery confirmed in 2020.
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- “Queta“, the name of this satellite is perhaps 0.6 miles across and circles Eurybates every 84 days. Queta is a much smaller piece of the same asteroid that Eurybates once belonged to.
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- Next, Lucy will have three quick flybys. First, in September 2027, “Polymele“, a smallish redder asteroid that may also represent a fragment of a larger lost rock.
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- Seven months later comes “Leucus“, with a weirdly slow spin that likely affects the asteroid's temperature.
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- Next comes “Orus“, the red member of the color-comparison pair that Lucy is built around.
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- The bulk of Lucy's flybys will come during just 15 months in late 2027 and 2028. All of these Trojans are in the “L4 swarm“, which runs ahead of Jupiter in its orbit.
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- After this burst of flybys, Lucy will head back toward the sun to complete another flyby of Earth, which will put the spacecraft on track to visit the “L5 swarm” following behind Jupiter in the early 2030s.
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- And in that swarm is another prize of the mission is a pair of rocks nearly the same size orbiting each other dubbed “Patroclus” and “Menoetius“, a binary which Lucy will fly past in 2033.
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- Such evenly sized binaries are rare in the inner solar system and main asteroid belt, where scientists can most easily study such rubble.
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- Observations out in the Kuiper Belt of small bodies beyond Neptune show that in this outer neighborhood where well-balanced binaries are quite common.
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- Out at that distance, the objects are essentially untouched. They are far enough away from the planetary system that the violence of planet formation never affected them.
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- The theory is that Patroclus and Menoetius is one of just a few formerly plentiful equal-mass binaries in the heart of the solar system to survive the havoc of the solar system's early days.
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- Patroclus and Menoetius will serve as a key contrast to the spacecraft's first Trojan, Eurybates. Going by one object that underwent a really massive collision and therefore was beginning to be involved in planet formation, and an object that we think is pristine.
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- Furthering the quest to learn , “ How did we get here?”
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- October 15, 2021 METEORITES - visits to learn origin of solar System? 3304
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